Core slabbing method

ABSTRACT

A geological core sample is slabbed by advancing the sample against a horizontally oriented bandsaw blade. A receiving tray positioned immediately adjacent and to the rear of the bandsaw blade provides continuous support to the upper portion of the slab as it is cut from the sample and maintains the integrity of friable and unconsolidated materials.

This is a division of co-pending application Ser. No. 556,797 filed onDec. 1, 1983 and now U.S. Pat. No. 4,628,894 issued Dec. 16, 1986.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for exposing aninterior surface of a stratigraphic sample, and in particular to amethod and apparatus which leaves undisturbed the physical and chemicalproperties of the exposed interior stratigraphy of such sample.

2. Description of the Prior Art

The study of geological strata generally involves the on-site collectionof geological samples and the removal of these samples to remotelaboratories for analysis. The geological material is typicallycollected in the form of an elongated cylindrical core which is encasedwithin a plastic sleeve or tube that is positioned within the boringshaft or pipe. (The term "sample" will hereinafter be used to refercollectively to both such a core and the sleeve in which it isenclosed.) Once in the laboratory, the sample is split along itslongitudinal axis to expose the interior stratigraphic profile of thecore material in a process which is commonly referred to as "slabbing".The longitudinal section thereby split off from the sample comprisingthe core material, with or without the section of the sleeve or tube isreferred to as a "slab".

The accuracy of the data acquired from the laboratory analysis of theslab depends to a large extent upon the degree to which the interiorstratigraphic profile is left undisturbed by the slabbing process.Disturbance to the interior stratigraphy poses a particular problem whenthe core is composed of material which is "friable" (i.e.. brittle) or"unconsolidated" (i.e., composed of loose gravel, sand or the like).

Several prior art methods have been employed for slabbing samples. Inone such method the sample is first oriented so that its longitudinalaxis is horizontal. A small horizontal knife blade is then passedseveral times through one side of the sample in a direction parallel tothe longitudinal axis. On the initial pass of the knife blade only theplastic tube surrounding the core is cut. On each subsequent pass theknife is guided slightly closer to the central axis of the core, theobjective being to divide the core gradually so as not to disturb itsinternal composition. After one side of the sample has been completelydivided, the sample is rotated 180 about its longitudinal axis and theslicing procedure is repeated on the opposite side. The sample is thenpulled apart into equal halves, thereby exposing the interiorstratigraphic profile.

Among the major disadvantages of the above method are the extensiveamount of time required to slab each sample and the limitation of themethod to cores of soft material, such as mud, sand, clays and the like.This limitation is due to the fact that the small blade used in thisprocess is incapable of splitting the larger rock fragments which may befound in the core. Instead the blade merely pushes these rock fragmentsthrough the core, causing undesired disturbance to the materialcomprising the core and thereby to the stratigraphic profile. Inaddition, this method provides no mechanism for supporting the freshlycut core material after each pass of the knife blade. If the corematerial is comprised of loose sand or gravel, the freshly cut interiorsurface will merely collapse as the knife passes through the core. Thismethod therefore can not be used to slab unconsolidated core material.

There is a variation of the above method in which a very broad knifeblade is passed once through the entire sample. The knife blade issufficiently broad so that as the slab is separated from the sample itis supported on the knife blade itself, thereby enabling the slabbing ofunconsolidated cores. However, this second method has the disadvantageof always requiring the use of a liquid lubricant (such as water,kerosene, brine solutions or the like) between the knife blade and thecore. A lubricant is necessary not only to prevent the knife fromsticking as it passes through the core, but also to prevent drag on theblade from distorting the interior surface of the slab as the cut isbeing made. The use of a lubricant is undesirable because of itstendency to distort both the physical and chemical integrity of the coreinterior. Additionally, the knife used in this second method isincapable of splitting larger rock fragments which may be contained inthe cores.

A third method of slabbing is used in which the sample is first frozenin dry ice. After freezing, the plastic tube is removed from the core bythe application of several sharp hammer blows which shatter the brittle,frozen plastic. The still frozen core is then wrapped with aluminum foiland placed within a thick-walled cardboard tube. An immobilizingcompound, such as epoxy resin, is then poured into the tube in order tocast the core and the core is left to cure. After the curing heatsubsides, the core is refrozen.

The frozen and immobilized core is then oriented vertically and dividedby drawing a radial blade saw down through the length of the core. Theresulting slab is recovered as it falls to the side.

This third method may be used for slabbing core material which isunconsolidated, since the loose contents of the core are held intact byfreezing and immobilization. Use of a radial blade saw also enables theslabbing of samples which contain large rock fragments. However, thisthird method is both time consuming and expensive, requiring the use ofboth an immobilizing compound and a liquid coolant (such as liquidnitrogen) to dissipate the heat generated and overcome the frictionencountered by the radial blade saw. Disturbance to the core interiormay occur at several points during the process, including the freezingand immobilizing of the core and the recovery of the unsupportedvertical slab as it falls away from the remaining core.

An objective of the present invention is therefore to provide methodsand apparatus for slabbing any sample, including one in which the corematerial is friable, unconsolidated, or contains large rock fragments,without distorting the physical structure or contaminating the chemicalcomposition of the core.

A further objective of the present invention is to provide methods andapparatus by which a sample may be slabbed directly as it is receivedfrom the field with minimum disturbance to the interior of the core.

A further objective of the present invention is to provide a method andapparatus for slabbing which does not require the use of liquid coolantsor liquid lubricants.

A further objective of the present invention is to provide a method andapparatus for slabbing which does not require that the sample be frozenor immobilized prior to being slabbed.

A further objective of the present invention is to provide a slabbingapparatus which is simple and inexpensive to construct and is reliablein operation.

SUMMARY OF THE INVENTION

In accordance with the present invention, these and other objectives areachieved by providing a bandsaw blade having a horizontally orientedcutting edge. A horizontally oriented sample is divided into an upperand lower portions by advancing the sample against the bandsaw blade.The upper portion of the slab thereby created is supported by areceiving tray positioned immediately adjacent and to the rear of thebandsaw blade.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of the invention will be made with reference tothe accompanying drawings, wherein like numerals designate correspondingparts in the several figures.

FIG. 1 is a perspective view of one embodiment of the present invention.

FIG. 2 is an end view of the embodiment shown in FIG. 1.

FIG. 3 is a side elevation of the embodiment shown in FIG. 1.

FIG. 4 is a fragmentary perspective view showing details of oneembodiment of the slab receiving means of the present invention.

FIG. 5 is a perspective view showing the slab in relation to thereceiving means.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description is of the best presently contemplatedmode of carrying out the invention. This description is not to be takenin a limiting sense, but is made merely for the purpose of illustratingthe general principles of the invention. The scope of the invention isbest defined by the appended claims.

Referring to FIGS. 1, 2, 3 and 4, the invention includes a bandsaw mainframe 2 which houses a bandsaw blade 4 having a continuous circulatingcutting edge 6. Any one of a number of commercially available bandsawmachines may be used for purposes of the present invention, including,for example, the Zephyr model number 75-3620 Do-All bandsaw machinemanufactured by the Do-All International Corporation, a subsidiary ofthe Do-All Company of Des Plaines, Ill.

The bandsaw main frame 2 is positioned so that the cutting edge 6 of thebandsaw blade 4 is oriented horizontally. The cutting edge 6 of thebandsaw blade 4 may be composed of any of a number of materials whichare commonly used for cutting minerals or metals, including diamond,tungsten, carbide, spring tempered steel, carborundum, and siliconcarbide. A pair of rollers 7a,b serve to guide and stabilize thehorizontal bandsaw blade 6 immediately prior to its contact with thesample 38 (FIG. 4).

The use of a horizontal bandsaw blade in the present invention providesseveral advantages over the cutting means (knives, wires, radial blades,etc.) used in the prior art. One such advantage is that the bandsawblade of the present invention is capable of cutting through extremelyhard objects, thereby enabling the slabbing of cores containing largerock fragments.

Another advantage of the bandsaw blade is that the frictional heatgenerated by contact between the sample and the cutting edge duringslabbing is dissipated along the entire length of the bandsaw blade.Experience has shown that, if the circumferential length of the bandsawblade is sufficiently large, the heat is adequately dissipated by thebandsaw blade alone and the need for additional liquid coolants orlubricants to maintain the blade at a safe operating temperature iscompletely eliminated. This in turn eliminates the undesirable coredistorting effects associated with such liquid coolants and lubricants.In the preferred embodiment, the circumferential length of the bandsawblade 4 is approximately nineteen feet. However, smaller bandsawmachines having proportionately small blades of eight feet may beemployed in the invention. The determining factor is whether the heatdissipating surface area of the blade is sufficient to prevent thetemperature of the blade from exceeding its maximum safety limits. Theamount of heat generated and therefore to be dissipated, will dependupon the size and composition of the samples as well as the type andcondition of the cutting edge. Fluid coolants such as liquid nitrogencould be employed.

Still another advantage of a horizontally oriented bandsaw blade is thatthe surface of the blade serves to support the upper portion of the coreslab immediately after the slab is separated from the sample, but beforethe slab is subsequently contacted and supported by a receiving tray ina manner described in further detail below. The use of horizontalcutting means thereby enables the entire slab to be fully supportedduring each step of the slabbing process, allowing the slabbing ofsamples containing friable-to-unconsolidated core material whilepreserving the integrity of the core interior.

Again referring to FIGS. 1, 2, 3 and 4, a horizontally oriented travelplate 8 is mounted perpendicular to the bandsaw main frame 2 so that thetravel plate 8 straddles the bandsaw blade 4. The travel plate 8 issupported by a base plate 10 which is also mounted on the bandsaw mainframe 2. The vertical position of the travel plate 8 with respect to thebandsaw blade 4 may be adjusted by means of a series of adjustment slots12, thereby enabling slabs of varying thickness to be cut. The baseplate 10 includes an upper edge 14 which extends several inches abovethe plane defined by the horizontal bandsaw blade 4.

Resting on the travel plate 8 is a sample holder 16. The sample holder16 is configured to hold a sample in place as the sample is advancedagainst the bandsaw blade 4, so that the same relative angularorientation between the sample 38 and the bandsaw blade 4 is maintainedthroughout the slabbing operation. The sample holder 16 rests in a guidetrack 18 which runs along the length of the travel bed 8 in a directionperpendicular to the bandsaw blade 4. The guide track 18 allows thesample retained within the sample holder 16 to be advanced across thebandsaw blade 4 smoothly and evenly. As shown most clearly in FIGS. 4and 5, a slab receiving tray 20 is disposed adjacent to and co-planarwith the bandsaw blade 4. The receiving tray 20 may be secured in thisposition by attaching it to the upper edge 14 of the base plate 10 bymeans of tray hooks 22 which engage clips 24 attached to the upper edge14.

One or more suction hoses 26 are positioned near the cutting edge 6 ofthe bandsaw blade 4. These suction hoses 26 are operationally connectedto a remote vacuum source 28 and operate to remove from the cutting siteextraneous material or "rock flour" which may be produced when thebandsaw blade 4 encounters brittle material in the sample 38. Thepartial vacuum produced by hoses 26 at the cutting site also causes astream of air to act as a fluid coolant as it passes over the blade 4,supplementing the heat dissipating effect of the bandsaw blade 4. Theneed for applying undesirable liquid coolants of the prior art isthereby eliminated.

A slabbing operation in accordance with the above-described embodimentof the present invention may proceed as follows:

A sample 38 comprising a geological core 40 which is enclosed within aplastic tube 42 is placed on the sample holder 16, thereby orienting thelongitudinal axis of the sample 38 so that it is substantially co-planarwith, and perpendicular to, the cutting edge 6. The operation of thebandsaw blade 4 is initiated by closing a switch 50, which completes acircuit between the bandsaw motor 52 and a power supply (not shown). Theoperation of the vacuum source 28 attached to suction hoses 26 is alsoinitiated at this time.

The sample holder 16 is than advanced along guide track 18, therebycausing the sample 38 to come into contact with the cutting edge 6 ofthe circulating bandsaw blade 4. As sample holder 16 is advanced, thecutting action of the bandsaw blade 4 will divide the sample 38 alongits longitudinal axis into two sections: an upper core section or "slab"44 and a lower core section or "bulk" 46 (FIGS. 4 and 5).

The receiving tray 20 is positioned to receive the advancing core slab44 immediately after its passes over the bandsaw blade 4. The advancingslab 44 is therefore always supported by either the bandsaw blade 4 orthe receiving tray 20 which is positioned immediately to the rear of,and in close proximity to the blade 4. The surface integrity of even themost unconsolidated core is thereby preserved. Once the sample 38 hasbeen completely divided, the receiving tray 20 contains the completedslab 44. The receiving tray 20 may be easily inverted to expose thefresh cut surface of the slab 44 for geological examination andphotography.

In addition, if immobilization of the completed slab 44 is desired, anonporous end cap 48 may be secured to the receiving end 49 of thereceiving tray 20. A leak proof container is thereby created into whichepoxy, plaster-of-paris, paraffin, or any other of a number of moldingcompounds may be poured in order to immobilize the slab 44.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Forexample, a sufficiently long horizontal reciprocating blade (similar toa rip-saw blade) may be used in substitution for the disclosed bandsawblade. The presently disclosed embodiments are therefore to beconsidered in all respects as illustrative and not restrictive, thescope of the invention being indicated by the appended claims ratherthan the foregoing description, and all changes which come within themeaning and range of equivalency of the claims are therefore intended tobe embraced therein.

What is claimed is:
 1. In the method for longitudinally dividing anelongated stratigraphic sample comprising a core enclosed within a tubeto thereby expose the interior of said core, the improvement whichcomprises the steps of:orienting a cutting means comprising a continuouscirculating cutting edge in a substantially horizontal plane,positioning the longitudinal axis of said sample in a planesubstantially parallel with said cutting edge, bringing said sample andsaid cutting edge into contact with one another to thereby divide saidsample into an upper section and a lower section, receiving said uppersection as said sample is divided in a receiving means positionedimmediately adjacent to and co-planar with said cutting means, andproviding continuous and uninterrupted support for said upper section assaid sample is divided, without deflecting said upper section from saidlower section, whereby the physical integrity of the interior surface ofthe sectioned core is preserved.
 2. The method of claim 1 which furthercomprises the step of immobilizing the upper section of the core afterit has been divided.
 3. The method of claim 2 which comprises applyingan immobilizing compound to the upper section of the core while it is insaid receiving means.
 4. A sectioned core produced in accordance withthe method of claim
 1. 5. An interior surface of a core exposed inaccordance with the method of claim
 1. 6. The method of claim 1 whereinthe cutting means has a sufficient heat dissipating area to maintain thetemperature of the cutting means within its safe operating range.
 7. Themethod of claim 6 wherein the cutting means comprises a bandsaw blade.8. The method of claim 1 wherein the cutting means are supported on astationary frame, and the sample is advanced into contact with thecutting means.
 9. The method of claim 8 where the receiving means ismaintained in a stationary position during the cutting and dividing ofthe sample.
 10. The method of claim 1 wherein a stream of fluid coolantis passed over the cutting means.
 11. The method of claim 10 wherein thestream of fluid coolant also provides an exhaust medium for removingextraneous core material generated by the cutting means.
 12. The methodof claim 1 which includes the further step of closing the receivingmeans to provide a container having a base and continuous upstandingwalls to a height that exceeds that of the upper surface of thesectioned core sample.
 13. The method of claim 3 in which the uppersection of the core is immobilized by application of an immobilizingcompound selected from the group of molding compounds consisting ofepoxy, plaster-of-paris and paraffin.